We reported previously the stimulatory effects of N6O2-dibutyryl adenosine 3',5'-monophosphate ((But)2cAMP) on axoplasmic flow and neurite development in vitro. To clarify the nucleotide's role and further our understanding of in vitro neuronal maturation we have examined the intracellular distribution of several contractile proteins. The distribution of intracellular myosin was studied by the double antibody immunofluorescence method in primary organotypic neuronal cultures and two established neuronal and glial cell lines. An array of parallel filaments aligned with the major cellular axis and a three-dimensional subsurface network were shown to react with two different myosin antibodies. The presence of myosin-rich filaments in regions known to contain actin filaments suggests that these proteins, in conjunction with a structural framework provided by the microtubules, interact to generate the motive force for axoplasmic flow and axonal elongation. The effects of (But)2cAMP on this interaction are currently under study. We have also studied the nucleotide's action in vivo and have shown that after crush lesion of sciatic nerves, rats treated with (But)2cAMP regain sensorimotor function more rapidly than saline controls. Our SEM and TEM studies have shown that the nucleotide accelerated the initial processes of Wallerian degeneration and enhanced the regeneration and maturation rates of the peripheral nerve fibers.